Refer to the exhibit.

What is preventing R4 from learning any networks via OSPF?

A.
R4 does not have any OSPF neighbors.

B.
There is no OSPF backup designated router on FastEthernet0/0.

C.
The OSPF area number for FastEthernet0/0 does not match the interface network.

D.
There are no OSPF learned routes in the network beyond R4.

Explanation:
As you can see in the exhibit, no OSPF neighbors are configured so R4 will not be able to learn
about networks via OSPF. There is no DR elected router so this is the only OSPF speaker on the
Ethernet segment.